There is lots of discussion about this on the board and there can be various reasons depending on your setup. The most likely reasons are (sorry no a lot of detail I'm away from my edison right now) :
- if you have an arduino setup you may have the usb host/device switch in the wrong position
- if you have a mini breakout board it is probably the way you supply power. You need to either supply power via the 2 pin .1"c-c power connector (not battery connector)or solder a barrel (power supply) connector on the back and supply power via that
Otherwise search the forum... there have been lots of threads about this.